[devel at bb.net] Mergeable Buildbot pull requests

[dustin at buildbot.net]

Mergeable pull requests:

https://github.com/buildbot/buildbot/pull/2257 - Git shallow depth
https://github.com/buildbot/buildbot/pull/2255 - remove reference api documentation generation scripts
https://github.com/buildbot/buildbot/pull/2252 - remove notion of removed source commands from worker
https://github.com/buildbot/buildbot/pull/2250 - remove worker's WorkerForBuilder.remote_shutdown()
https://github.com/buildbot/buildbot/pull/2248 - update master/worker API docs
https://github.com/buildbot/buildbot/pull/2138 - Run Sphinx' linkcheck on Travis + fix incorrect links